The goal of this proposal is to identify biosynthetic enzymes catalyzing reactions leading to the formation of gossypol in the cotton plant. Information of this kind can be useful in the genetic removal of gossypol from Gossypium hirsutum through the selection of mutants lacking these enzymes. The proposal calls for the purification and structure analysis of a cotton root prenyltransferase which catalyzes the formation of farnesylpyrophosphate and a cotton root cyclase which utilizes the farnesylprophosphate in the formation of a cyclic sesquiterpenoid, a precursor of gossypol. In addition, experiments are proposed which can establish if gossypol is a phytoalexin, and if this phytoalexin property is due to a de novo synthesis of gossypol or simply a formation of a "free"-active form of gossypol from an inactive precursor or storage form.